A test system is indispensable for guaranteeing quality of semiconductor devices and other electronic parts and for improving the manufacturing process thereof. While there are many semiconductor test systems in the market (ex. 9480A, 9490 and others manufactured by Yokogawa and Hewlett Packard), an advanced inspection technology is needed.
Because of progress in semiconductor technology relevant design rules, degree of integration and number of pins of I/O tend to increase every year. For example, a gate array having more than 1000 pins and less than 70 micron of pitch is expected to appear in the next few years as shown in FIG. 23 (see "Study on Multi-pin Probe Card" by Ryoichi Takagi, Masahiro Ueda and Tetsuo Tada, National Convention of the Institute of Electronics Information and Communication Engineers (Spring), C-641, 1990). Such rapid increase of the number of terminals and miniaturization of size of terminals will make it more difficult to probe wafer terminal pads in testing them and to probe terminal pins in testing multi-pin high density LSI packages.
In a conventional wire type probe used in a wafer probing apparatus, probe needles (73) are secured on a wired rigid epoxy probe substrate (71) by a ring (72) as shown in FIG. 24. This probe is used in characteristic tests of semiconductor devices by contacting the point of the probe and flowing test signals directly to terminals of the semiconductor device to be measured. While such probes provide some advantages, some limitations remain.
It is difficult to package the probe needles on the substrate in multi-pin narrow pitch because a diameter of the needles is thick. Accordingly, it is difficult to use such a probe to probe wafers having more than 500 terminals, less than 100 micron pitch, and small terminal pad size. Thinning of the probe needles is limited in conventional processing technology.
However, even if the probe needle is thinned by employing a special processing technology, such thinning creates new difficulties. For example, wear due to several tens of thousands times of touchdown increases a contact resistance between the needle point and the terminal of the semiconductor device. Accordingly, it becomes difficult to obtain a stable conductivity. Also cracks are readily created at the needle points. Furthermore, regular cleaning and polishing of the needle points are required because debris of the terminal pads attaches and deposits on the needle points and because the needle points are also abraded.
One of the problems of the wire type probe lies also in its manufacturing method. That is, such probe is manufactured by a method wherein probe needles are adhered and secured one by one, adjusting to positions of terminals of a semiconductor device such as a LSI chip to be inspected. Accordingly, its manufacturing cost increases in proportion to an increase of the number of pins of semiconductor device. Furthermore, a skilled craftsman is required to manufacture such a probe, which limits manufacturing productivity.
By their very nature, such probes need to be reformed for each semiconductor device to accommodate various changes of terminal position and terminal pad size, various changes of size of chip itself, and various changes of semiconductor devices. Such reformation considerably increases total cost, including design cost.
Furthermore, electrical performance of such probes is generally limited, especially for high speed signals.
Though a pitch of probe needles is narrowed down as a pitch of terminals to be probed is narrowed down, a certain degree of length of the needles is still necessary. The length of the needles generally ranges to several centimeters. Due thereto, various problems arise in high frequency characteristic tests of a semiconductor device which operates in high speed. Noise is generated due to a self-inductance of the probe needles, which increases along the thinning of the diameter. Cross-talk between the probe needles increases along the decrease of the pitch of the probe needles. Transmission loss increases due to mismatching of impedances.
On the other hand, a singular wire type probe that can accommodate high frequency waves has been developed. Generally short probe needles are used in this probe, so that the aforementioned problems of the cross-talk and mismatching of impedances are eased. However, it cannot be applied to multi-pin narrow pitch semiconductor devices because a plurality needles are not mounted in bundle as in the case of the wire type probe and because it is used singularly.
Thus it has been very difficult for the conventional wire type probe to accommodate with both multi-pin narrow semiconductor devices and high speed and high frequency semiconductor devices. In order to solve such problems, a membrane probe has been proposed (see International Test Conference Proceedings, IEEE, 1988, pp. 601-607). Line patterns and projecting electrodes (contact bumps) made from metal thin film are formed on the surface of flexible insulative resin film, such as polyimide, using photolithography technology.
Another type of probe is a membrane probe as shown in FIG. 25, wherein contact bumps (83) are formed projecting at the portions where communicating holes (82) are created on one surface of an insulative synthetic resin film (dielectric film) (81). A ground layer (85) is formed on the side where the contact bumps are formed.
The membrane probe can accommodate with a wafer chip having more than 500 terminals and less than 100 micron pitch. An example of a prototype of membrane probe which accommodates with a chip having more than several hundreds pads and less than 100 micron of pitch has been reported.
The contact bumps are analogous to the probe needles of the wire probe shown discussed previously herein. Transmission and receiving of test signals are carried out by contacting them to terminals of a semiconductor device via the line pattern. Because the diameter of the contact bumps is so small as about several tens of microns (i.e. the height of the projection is about a half thereof) as compared to the wire probe, almost no influence of the self-inductance and cross-talk is seen in this portion. Further, because the transmission paths can be structured into a micro-strip line structure which allows match impedance, it is possible to test with less distortion of waveform and cross-talk caused by reflection even when transmitting high speed signals. Still more, it is possible to minimize the cross-talk and transmission loss by providing the ground layer and by optimally designing the width of transmission lines and the pitch between the transmission lines.
However, the membrane probe described above has limitations because it is manufactured using a photolithographic technology, metallic materials cannot be freely selected and that it is difficult to implement such a process as hardening, differing from the case when probe needles are used. That is, metals which can be selected are limited for such a process as plating often used in creating the bumps and a high temperature heat process cannot be implemented because a synthetic resin film is used. Accordingly, the membrane probe is limited in terms of the high hardening of the contact bumps and has a problem in its durability.
As for the durability, there is a problem not only in the contact bumps, but also in the synthetic resin film. Generally, a material such as polyimide is often used for the synthetic resin film, but such synthetic resin film readily decomposes and changes its hardness and elastic modulus depending on an environment.
Because the wire probe can be used almost semi-permanently except the case when cracks and abrasion of the needle point are caused, the durability of the membrane probe is predicted to be inferior as compared to the wire probe. In order to solve these problems, it is conceivable to mass produce disposable membrane probes taking advantage of the photolithographic technology. Presently, however, the manufacturing cost of the membrane probe per sheet is high and it is not widely used.
The largest disadvantage of the membrane probe is its manufacturing cost. As with the wire probe, the membrane probe also needs to be reformed for each semiconductor device to accommodate with changes of position and size of pads and changes of size of semiconductor device itself. This means that masks for photolithography need be reformed and normally, at least three or four masks need to be re-designed and re-manufactured. Although the photolithographic technology is suited for producing the same item in a large quantity and economies of scale provide cost reductions, the cost becomes higher when the process needs to be built for each semiconducter device.
Although the cost of the membrane probe will not become high in proportional to the increase of the number of pins, differing from the wire probe, the cost of the membrane probe is almost the same or higher than that of the wire probe when the number of pins is around 500. The merit of the cost of this method is considered to appear when the number of pins is more than 1000.
As pointed out previously, conventional probes such as the wire probe and the membrane probe are custom designed or re-formed for each semiconductor device. However, a semiconductor device manufacturer often will not disclose the information needed to create the probe design, such as size of chip and arrangement of pads. This is because technology level of the device can be estimated from the size of chip, the number of I/O pins, and arrangement of pads. Accordingly, such disclosure is contrary to security interests of the semiconductor device manufacturer and their wish to keep an advantage in competition with other manufacturers.
As discussed herein, among the conventional probes, the wire probe has limitations in probing multi-pin narrow pitch devices and those which operate at high speeds and at high frequencies. Although the membrane probe using photolithographic technology can accommodate probing of multi-pin narrow pitch devices and of those which operate in high speed and in high frequency, its cost is high because photo-masks need to be reformed and process needs to be rebuilt for each semiconductor device, resulting in increased manufacturing and maintenance costs. What is needed is a probe that provides durable, high performance probing of narrow pitch devices, but does not require a separate probe to be manufactured for each one of various sizes and pad arrangements of the devices.